A 7b 1GS/s 7.2mW nonbinary 2b/cycle SAR ADC with register-to-DAC direct control

A 45nm CMOS 7b nonbinary 2b/cycle SAR ADC that operates up to 1GS/s with a 1.25V supply is presented. Use of a nonbinary decision scheme for decision error correction in a 2b/cycle structure not only increases the ADC speed with a relaxed DAC settling requirement but also makes the performance robust to reference fluctuation and signal-dependent comparator offset variation. Proposed dynamic registers and a register-to-DAC direct control scheme enhance the conversion speed by minimizing logic delay in the decision loop. At a sampling rate of 1 GS/s, the chip achieves a peak SNDR of 41.6dB and maintains ENOB higher than 6b up to 1.3GHz signal frequency. The FoM is 80fJ/ conversion-step at 1GS/s with a power consumption of 7.2mW.